From U.S. Pat. No. 3,858,416, Eugene F. White and Frances H. White, a yarn supply apparatus is known, the yarn supply element of which comprises a cylindrical disc mounted on the shaft of an electric drive motor. The yarn that is to be supplied is looped several times around the circumferential surface of the disk in such a manner that slip free yarn supply is assured. An electric motor is provided as the drive motor, its speed being regulatable by varying the supply voltage, in one embodiment, and by control of the pulses supplying the motor, in another embodiment. Via the drive motor, the speed of the yarn supply disk is synchronized with the speed of the circular knitting machine equipped with this kind of yarn supply apparatus. To this end, a pulse transducer is coupled with the revolving cylinder of the circular knitting machine and emits an output signal in pulse form which is representative of the machine speed. This output signal is converted by a frequency/voltage converter into an analog voltage, which is compared with the output signal that is emitted by a tachometer generator or incremental transducer connected with the drive motor and has been converted into a corresponding voltage. By means of a regulator, when a control deviation occurs the speed of the yarn supply disk is regulated to the command value predetermined by the pulse transducer of the circular knitting machine.
In this yarn supply apparatus, in order to maintain the tension of the yarn supplied to the needles at a predetermined value, a tension sensing means, or feeler, is provided following the yarn supply disk in the direction of yarn travel. Together with a command value source, the output of the feeler can be selectively sent to the regulator input by switch actuation, and by correspondingly controlling the drive motor the regulator establishes the tension value corresponding to the predetermined command value.
In circular knitting machines operating with striping devices, it sometimes happens that the yarn supply apparatus associated with a knitting feed must supply yarns according to a pattern during one or more revolutions of the machine, and that the yarn supply is abruptly interrupted temporarily. This means that the yarn supply must be effected synchronously with the changes in the operating status of the particular stripping device. Jacquard knitting machines, as well, generally operate with a different, constantly varying yarn requirement in the individual knitting feeds, in accordance with a pattern. To supply yarn, yarn storage fournisseurs must accordingly be used, with the yarn being pulled off over-end, or over-head, from the yarn storage drum as needed. Positive yarn supply is not possible with these fournisseurs.
For all these applications, in which a highly fluctuating amount of yarn is pulled off per unit of time at the individual knitting feeds, yarn supply apparatus which must be synchronized with an external pulse source, formed for instance as a pulse transducer rigidly joined to the cylinder of a circular knitting machine, is unsuitable.